Cable for use in safety barrier

ABSTRACT

A cable for use in a safety barrier is provided. A cable for use in a safety barrier may include a plastic core wire and a plurality of metal wires disposed adjacent to and longitudinally to the plastic core wire. The cable may be pre-stretched prior to installation in the safety barrier. A method of making cable for use in a safety barrier may include (a)providing a plastic core wire, (b) disposing a plurality of metal wires, each metal wire disposed adjacent to and longitudinally to the plastic core wire, and (c) prestretching the cable prior to installation in the safety barrier.

RELATED APPLICATION

This application is related to co-pending U.S. patent application Ser.No. 11/207,239 entitled “Cable Safety System,” filed Aug. 19, 2005.

TECHNICAL FIELD

The present disclosure is related to highway barriers and safety systemsand more particularly to cable safety systems and associated cables.

BACKGROUND OF THE DISCLOSURE

Cable safety systems and cable barriers have been installed along edgesof roadways and highways for many years. Cable safety systems and cablebarriers have also been installed along medians between roadways and/orhighways. Cable safety systems generally include one or more horizontalcables attached to support posts. For some applications cable safetysystems and cable barriers may reduce damage to an impacting vehicleand/or injury to occupants of the impacting vehicle as compared withother types of highway safety systems and highway barriers.

Cable safety systems are often designed and installed with at least onecable mounted horizontally on a plurality of generally vertical supportposts. Many cable safety systems include three cables spaced verticallyfrom each other on each support post. The number of cables may varydepending on factors such as the type of vehicles using the associatedroadway and the hazard which requires installation of the cable safetysystem. The length of a cable safety system is generally determinedbased on the adjacent roadside hazard. Each cable is typically installedat a selected height relative to the ground and with selected verticalspacing between adjacent cables.

During the past several years, cable safety systems have been used as analternative to traditional W-beam or thrie-beam guardrail systems. Cablesafety systems are often more aesthetically appealing and minimizepotential sight distance problems as compared with W-beam and thrie beamguardrail systems. Cable safety systems generally minimize snowaccumulation on adjacent highways and roadways.

As steel prices have increased, there has arisen a need to manufacturecable safety systems with lesser amounts of steel. However, an approachof lowering steel content by merely making steel cables thinner may notbe an appropriate solution, as such an approach may lower theeffectiveness of cable safety systems in protecting occupants of animpacting vehicle. Accordingly, solutions are needed in which steelcontent is reduced while at the same time maintaining the effectivenessof the cable safety system in reducing damage to impacting vehiclesand/or the occupants thereof.

SUMMARY OF THE DISCLOSURE

In accordance with teachings of the present disclosure, a cable safetysystem may be provided which overcomes many disadvantages and problemsassociated with prior cable safety systems and cable barriers.

According to one embodiment of the present disclosure, a safety barrierinstalled adjacent to a roadway comprising includes a plurality of postsspaced from each other and disposed adjacent to the roadway, and atleast one cable releasably engaged with and supported by the posts. Thecable may include a plastic core wire and a plurality of metal wiresdisposed adjacent to and longitudinally to the plastic core wire. Thecable may be pre-stretched prior to installation in the safety barrier.

According to another embodiment of the present disclosure, a cable foruse in a safety barrier may include a plastic core wire and a pluralityof metal wires disposed adjacent to and longitudinally to the plasticcore wire. The cable may be pre-stretched prior to installation in thesafety barrier.

According to yet another embodiment of the present disclosure, a methodof making cable for use in a safety barrier is provided. The method mayinclude providing a plastic core wire. A plurality of metal wires mayeach be disposed adjacent to and longitudinally to the plastic corewire. The cable may be pre-stretched prior to installation in the safetybarrier.

Further technical benefits of the present disclosure may includeimproved cables for use in safety barriers, wherein the cables may belighter than similar cables manufactured entirely from metal, while atthe same time remaining as effective against impacting vehicles assimilar cables manufactured entirely from metal. Other technicaladvantages and benefits will be apparent to those of ordinary skill inthe art in view of the following specification, claims, and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete and thorough understanding of the present disclosure andadvantages thereof may be acquired by referring to the followingdescription taken in conjunction with the accompanying drawings, inwhich like reference numbers indicate like features, and wherein:

FIG. 1 a is a schematic drawing in elevation with portions broken awayof a cable safety system, in accordance with the present disclosure;

FIG. 1 b is a schematic drawing showing a plan view with portions brokenaway of the cable safety system of FIG. 1 a;

FIG. 1 c is a schematic drawing in elevation with portions broken awayof another cable safety system incorporating teachings of the presentdisclosure;

FIG. 1 d is a schematic drawing in section and in elevation withportions broken away of a below ground cable anchor assemblysatisfactory for use with the cable safety system of FIG. 1 c;

FIG. 2 is a schematic drawing showing an isometric view with portionsbroken away of a post and cables, in accordance with the presentdisclosure;

FIG. 3 a is a schematic drawing in section showing one example of acable formed using a seven strand metal wire rope, in accordance withthe present disclosure;

FIG. 3 b is a schematic drawing in section depicting the forces that maybe applied during an impact to individual wires of the wire rope of FIG.3 a;

FIG. 4 a is a schematic drawing in section showing one example of acable formed using a plastic core wire surrounded by a plurality ofmetal wires adjacent to and disposed longitudinally to the plastic corewire, in accordance with the present disclosure;

FIG. 4 b is a schematic drawing in section depicting the forces that maybe applied during an impact to the individual wires of the wire rope ofFIG. 4 a;

FIG. 5 a is a schematic drawing in section showing one example of acable formed from three groups of seven strand metal wire rope, inaccording with the present disclosure;

FIG. 5 b is a schematic drawing in section showing one example of acable formed from three groups of wire rope, each of the three groupsformed using a plastic core wire surrounded by a plurality of metalwires adjacent to and disposed longitudinally to the plastic core wire,in accordance with the present disclosure; and

FIG. 5 c is a schematic drawing in section showing one example of acable formed from three groups of wire rope, wherein one of the threegroups is formed using a plastic core wire surrounded by a plurality ofmetal wires adjacent to and disposed longitudinally to the plastic corewire, in accordance with the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the invention and its advantages are bestunderstood by reference to FIGS. 1 a-11 wherein like reference numbersindicate like features.

The terms “safety system” or “safety systems”, “safety barrier” or“safety barriers,” and “barrier” or “barriers” may be used throughoutthis application to include any type of safety system and/or barrierwhich may be formed at least in part using cables and support postsincorporating teachings of the present disclosure. The term “roadway”may be used throughout this application to include any highway, roadwayor path satisfactory for vehicle traffic. Safety systems and barriersincorporating teachings of the present disclosure may be installed inmedian strips or along shoulders of highways, roadways or any other pathwhich is likely to encounter vehicular traffic.

Various aspects of the present disclosure will be described with respectto cable safety systems 20 and 20 a. However, teachings of the presentdisclosure may be used to form a wide variety of safety systems andbarriers. Cable safety systems 20 and 20 a may have similar designfeatures and characteristics except cable safety system 20 includesabove ground anchors 24 and 26. Cable safety system 20 a includes belowground anchors 24 a and 26a. The present disclosure is not limited tocable safety systems 20 and 20 a as shown in FIGS. 1 a-1 d.

Cable safety systems 20 and 20 a may be installed adjacent to a roadway(not expressly shown) to prevent motor vehicles (not expressly shown)from leaving the roadway and to redirect vehicles away from hazardousareas without causing serious injuries to the vehicle's occupants orother motorists. The general direction of traffic flow along the roadwayis illustrated by directional arrow 22.

Cable safety systems 20 and 20 a may be satisfactorily used as a median,a single barrier installation along the edge of a roadway and at mergeapplications between adjacent roadways. For some applications, cablesafety systems 20 and 20 a may satisfactorily withstand a second impactbefore repairs have been made after a first impact. For manyapplications, cable safety systems 20 and 20 a may be described asgenerally maintenance free except for repairs required after a vehicleimpact.

Cable safety systems 20 and 20 a preferably include a plurality ofsupport posts 30 anchored adjacent to the roadway. Posts 30 may beanchored with the ground using various techniques. For some applicationsa concrete foundation (not expressly shown) may be provided with holesto allow relatively quick and easy insertion and removal of parts. Thenumber, size, shape and configuration of posts 30 may vary significantlyamong various applications and installations. Optimum spacing betweenposts 30 may also vary among various applications and installations.See, for example, U.S. Pat. No. 6,962,328, granted Nov. 8, 2005 andentitled “Cable Safety Systems,” which is incorporated by referenceherein for all purposes.

Various types of cables and/or wire ropes may be satisfactorily used toform a cable safety system in accordance with teachings of the presentdisclosure. Cables 160 a, 160 b and 160 c may be substantiallyidentical. However, for some applications each cable of a cable safetysystem formed in accordance with teachings of the present disclosure mayhave different characteristics. Cable safety systems 20 and 20 a may begenerally described as flexible, substantially maintenance free systemswith designed low deflection of cables 160 a, 160 b, and 160 c during avehicle impact. Forming cable safety systems 20 and 20 a in accordancewith teachings of the present disclosure minimizes damage during avehicle impact with posts 30 and/or cables 160 a, 160 b and 160 c. Forsome applications cables 160 a, 160 b and 160 c may be formed from sevenstrand wire rope, e.g. cable 170 as depicted in FIG. 3 a. Other types ofwire ropes and cables may also be used, e.g., cable 175 as depicted inFIG. 4 a, cable 180 depicted in FIG. 5 a, cable 190 depicted in FIG. 5b, and/or cable 195 as depicted in FIG. 5 c.

A plurality of cables 160 a, 160 b and 160 c may be attached to supportposts 30 in accordance with teachings of the present disclosure. Supportposts 30 generally maintain associated cables 160 a, 160 b and 160 c insubstantially horizontal positions extending along an edge of theroadway. Support posts 30 often allow relative quick and easy repair ofcable safety systems 20 and 20 a after a vehicle impact.

Cable safety systems 20 and 20 a are generally relatively narrow ascompared to conventional W-beam and thrie beam guardrail systems. Thelength of cables 160 a, 160 b and 160 c may be up to 3,000 metersbetween anchors 24 and 26 or anchors 24 a and 26 a. For otherapplications the length of cable 160 a, 160 b and 160 c may exceed 3,000meters without an intermediate anchorage. Support posts 30 maintaindesired vertical spacing between cables 160 a, 160 b and 160 c anddesired vertical spacing of each cable relative to the ground. Cablesafety system 20 and 20 a including support posts 30 formed inaccordance with teachings of the present disclosure may be designed inaccordance with teachings of the present disclosure to meet or exceedthe criteria of NCHRP Report 350 Level 3 requirements.

Cable safety systems 20 and 20 a preferably include cables 160 a, 160 band 160 c disposed in slot 40 of each post 30. Cable 160 a, 160 b and160 c are preferably disposed at different heights relative to theground and relative to each other. Varying the vertical spacing betweencables 160 a, 160 b and 160 c often provides a much wider lateral catcharea for vehicles impacting with cable safety systems 20 and 20 a. Thevertical spacing between cables 160 a, 160 b and 160 c may be selectedto satisfactorily contain both pickups and, to some extent, even largervehicles with a relatively high center of gravity, as well as vehicleswith a low front profile and low center of gravity.

Cables 160 a, 160 b and 160 c may be prefabricated in approximatelythree hundred (300) meter lengths with desired fittings attached withopposite ends of each cables 160 a, 160 b and 160 c. Tailor made cables160 a, 160 b and 160 c may then be delivered to a desired location forinstallation adjacent to a roadway.

Alternatively, cables 160 a, 160 b, and 160 c may be formed from asingle cable stored on a large drum (not expressly shown). Cables storedon drums may often exceed three thousand (3,000) meters in length.Cables 160 a, 160 b, and 160 c may be cut in desired lengths from thecable stored on the drum. Appropriate fittings (not expressly shown) maybe swaged or otherwise attached with opposite ends of the respectivecable 160 a, 160 b and 160 c at an onsite location. Cables 160 a, 160 band 160 c may be installed between anchors 24 and 26 or anchor 24 a and26 a with approximately twenty thousand Newtons of tension over a lengthof approximately three thousand (3,000) meters.

FIG. 1 d shows one example of a below ground anchor which may besatisfactorily used with a cable safety system incorporating teachingsof the present disclosure. Respective holes 27 may be formed in theground at desired locations for anchors 24 a and 26 a. A portion of eachhole 27 may be filled with concrete foundation 28. Anchor plate 29 maybe securely engaged with concrete foundation 28 using various types ofmechanical fasteners, including, but not limited to, a plurality ofbolts 23 and nuts 24. Anchor plate 29 may be formed at an appropriateangle to accommodate the design of cable safety system 20 a. Alsomultiple slots and/or openings (not expressly shown) may be formed inanchor plate 29 to receive respective end fittings 64.

For the embodiment of the present disclosure as shown in FIG. 1 d, endfitting 64 a of cable 160 a is shown engaged with anchor plate 29.Various types of anchor assemblies and cable end fittings may besatisfactorily used with a cable safety system incorporating teachingsof the present disclosure. The present disclosure is not limited toanchor 24 a or end fittings 64 a as shown in FIG. 1 d.

One example of support posts 30 and cables 160 a, 160 b and 160 c whichmay be satisfactorily used to form cable safety system 20 in accordancewith teachings of the present disclosure is shown in FIG. 2. Post 30includes first end 31 and second end 32. For this embodiment of thepresent disclosure, post 30 includes a generally C-shaped cross sectiondefined in part by web 34 with respective legs 35 and 36 extendingtherefrom. As shown in FIG. 2, the extreme edge of each leg 35 and 36opposite from web 34 may be rounded or bent inward to eliminate anysharp edges. Support post 30 may also have a generally “rounded” or“soft” profile. For some applications post 30 may be formed using rollforming techniques.

Slot 40 is preferably formed in web 34 extending from first end 31towards second end 32. The length of slot 40 may be selected in partbased on desired vertical spacing of cable 160 c relative to theadjacent roadway. The length of slot 40 may also be selected toaccommodate the number of cables which will be installed therein anddesired vertical spacing between each cable. Slot 40 may have agenerally elongated U-shaped configuration defined in part by first edge41, second edge 42 and bottom (not expressly shown). For the embodimentof the present disclosure as shown in FIG. 2, first edge 41 and secondedge 42 may have a generally smooth profile and extend generallyparallel with each other. Forming slot 40 within web 34 of post 30eliminates requirements for bolts, hooks or other mechanical attachmentsto releasably secure cables 160 a, 160 b and 160 c with post 30. Furtherexamples of support posts 30 and cables 160 a, 160 b, and 160 c that maybe used to form cable safety system in accordance with the presentdisclosure may be set forth U.S. Pat. No. 6,962,328, discussed above.

FIG. 3 a is a schematic drawing in section showing one example of acable 170 for use in cable barrier system 20. Cable 170, as depicted,may comprise a metal core wire 71, and a plurality of metal wires 72disposed adjacent to and longitudinally to metal core wire 71. In someembodiments, cable 170 may comprise a seven strand wire rope. In thesame or alternative embodiments, metal core wire 71 and/or metal wires72 may comprise steel. FIG. 3 b depicts the forces that may be appliedduring an impact to individual wires 71, 72 of cable 170 during avehicle impact to cable safety system 20 comprising cable 170. As shown,a vehicle impact to cable safety system 20 may cause metal wires 72 tobe forced towards metal core wire 71, thus decreasing the flexibility ofcable 170.

In order to increase the flexibility of cable 170 depicted in FIG. 3 a,a plastic core wire 73 may be substituted in place of metal core wire71, as depicted in FIG. 4 a, forming cable 175. As shown in FIG. 4 a,cable 175 may include a plastic core wire 73 and a plurality of metalwires 72 disposed adjacent to and longitudinally to plastic core wire73. In certain embodiments, plastic core wire 73 may comprisepolypropylene. In the same or alternative embodiments, cable 175 maycomprise six metal wires 72. In addition, cable 175 may be manufacturedor formed by methods similar to that of cable 170.

FIG. 4 b depicts the forces that may be applied during an impact toindividual wires 72, 73 of cable 175 during a vehicle impact to cablesafety system 20 comprising 175. As shown, a vehicle impact to cablesafety system 20 may cause some of metal wires 72 (e.g. metal wires 72d, 72 e and 72 f) to be forced towards plastic core wire 73, while othermetal wires (e.g. metal wires 72 a, 72 b, and 72 c) may be forced awayfrom plastic core wire 73, due to the flexible nature of plastic corewire 73. Accordingly, cable 175 may remain more flexible during avehicle impact with cable safety system 20, and thus may be moreresistant to breaking than a similarly-sized metal-wire-only cable 170.

In certain embodiments, cables comprising three groups of seven-strandwire, for example, cables 180, 190 and 195 depicted in FIGS. 5 a, 5 band 5 c, respectively, may be used to form cable safety system 20. FIG.5 a depicts a cable 180 formed from three groups of seven strand metalwire rope, as is often used in conventional cable safety systems. Duringa vehicle impact to cable safety system 20 comprising cable 180, themetal wires 72 comprising each wire rope of cable 180 may be forcedtowards the metal core wire 71 of their respective wire rope, asdepicted in FIG. 3 b, which may result in decreased flexibility.

To increase the flexibility of a cable formed from three groups of sevenstrand wire rope, a plastic core wire 73 may be substituted in placeeach wire rope's metal core wire 71, as depicted in FIG. 5 b, formingcable 190. As shown in FIG. 5 b, cable 190 may include three wire ropes,each including a plastic core wire 73 and a plurality of metal wires 72disposed adjacent to and longitudinally to the respective plastic corewires 73. In a vehicle impact to a cable safety system 20 comprisingcable 190, some of the metal wires 72 of each wire rope comprising cable190 may be forced towards their respective plastic core wires 73, whileother metal wires 72 may be forced away from their respective plasticcores wires, as depicted in FIG. 4 b. Accordingly, cable 190 may remainmore flexible during a vehicle impact with cable safety system 20, andthus may be more resistant to breaking than a similarly-sizedmetal-wire-only cable 180.

In addition to the embodiments depicted in FIGS. 5 a and 5 b, cablesafety system 20 may comprise three groups of seven strand wire ropes,wherein some of the groups may include a plastic core wire 73, whileothers may not, such as cable 195 depicted in FIG. 5 c.

In conventional cable safety systems, cables are often pre-stretched toabout 50% of designed or rated breaking strength in order to obtain adesired modulus of elasticity for the cable. However, in accordance withthe present disclosure, cables 170, 175, 180, 190 and 195 may bepre-stretched to between approximately 60% and approximately 70% ofdesigned or rated breaking strength. Such increased pre-stretching mayreduce elasticity of the cable, thus decreasing the amount of deflectionof the cable during a vehicle impact, as compared to a cablepre-stretched to 50% of its breaking strength. In certain embodiments,increased prestretching to between 60% and approximately 70% of designedor rated breaking strength may permit use of smaller-diameter cables ascompared to that of conventional cable safety systems, thus potentiallyreducing raw materials cost.

Some of the advantages of the various alternatives discussed above maybe illustrated in TABLE 1.

TABLE 1 20 steel 18 steel wires, 1 wires, 3 plastic plastic 21 steelcore core wires; wire; wires; 21 steel 60%-70% 60%-70% 60%-70% wires;50% pre- pre- pre- pre-stretch stretch stretch stretch force force forceforce (conventional) (FIG. 5a) (FIG. 5c) (FIG. 5b) Wire 3.00 mm 2.81 mm2.88 mm 3.06 mm diameter Cable 19.00 mm 18.12 mm 18.58 mm 18.12 mmdiameter Tensile 1370 N/mm² 1570 N/mm² 1570 N/mm² 1570 N/mm² strengthMinimum 183.00 KN 184.00 KN 183.16 KN 183.69 KN breaking load Weight1.18 Kg/m 1.04 Kg/m 1.04 Kg/m 1.06 Kg/m of metal

The second column of TABLE 1 depicts the wire diameter, cable diameter,tensile strength, minimum breaking load, and weight of metal for anexample conventional cable 180 comprising three groups of seven-strandsteel wire rope. The third, fourth, and fifth each depict the sameparameters for alternatively constructed cables having a similar minimumbreaking load. Specifically, the third, fourth, and fifth columnsrespectively depict these same parameters for each of: (a) a 21 steelwire strand cable 180 similar to that depicted in FIG. 5 a pre-stretchedto 60% to 70%, (b) a 20 steel wire, 1 plastic core wire cable 195similar to that depicted in FIG. 5 c pre-stretched to 60% to 70%, and(c) a 18 steel wire, 3 plastic core wire cable 190 similar to thatdepicted in FIG. 5 b pre-stretched to 60% to 70%. From TABLE 1, it canbe seen that by using pre-stretched cables, lighter steel strands, andplastic core wire strands, cables of similar minimum breaking load tothat of conventional cables may be constructed using less metal, andtherefore, may be less expensive to manufacture.

Although the present disclosure and its advantages have been describedin detail, it should be understood that various changes, substitutionsand alternations can be made herein without departing from the spiritand scope of the disclosure as defined by the following claims.

1. A safety barrier installed adjacent to a roadway comprising: aplurality of posts spaced from each other and disposed adjacent to theroadway; and at least one pre-stretched cable releasably engaged withand supported by the posts; and the cable having a first plastic corewire, a first plurality of metal wires disposed adjacent to andextending longitudinally along the first plastic core wire.
 2. Thesafety barrier of claim 1, further comprising the cable pre-stretchedusing a force equal to between approximately 60% to approximately 70% ofthe force required to break the cable.
 3. The safety barrier of claim 1,wherein the first plastic core wire comprises a polypropylene thread. 4.The safety barrier of claim 1, wherein the first plurality of metalwires comprises six metal wires.
 5. The safety barrier of claim 1,further comprising: a first wire rope having the first plastic core andthe first plurality of metal wires; and a second wire rope and a thirdwire rope disposed adjacent to and extending longitudinally along thefirst wire rope.
 6. The safety barrier of claim 5, wherein at least oneof the second wire rope and third wire rope comprises: a plastic corewire; and a plurality of metal wires disposed adjacent to and extendinglongitudinally along the plastic core wire.
 7. The safety barrier ofclaim 5, wherein at least one of the second wire rope and third wirerope comprises: a metal core wire; and a plurality of metal wiresdisposed adjacent to and extending longitudinally along the metal corewire.
 8. A cable for use in a safety barrier comprising: a first plasticcore wire; a first plurality of metal wires disposed adjacent to andlongitudinally to the first plastic core wire; and the cablepre-stretched prior to installation in the safety barrier.
 9. The cableof claim 8, comprising the cable pre-stretched using a force equal tobetween approximately 60% to approximately 70% of the force required tobreak the cable.
 10. The cable of claim 8, wherein the first plasticcore wire comprises a polypropylene thread.
 11. The cable of claim 8,wherein the first plurality of metal wires comprises six metal wires.12. The cable of claim 8, further comprising: a first wire rope havingthe first plastic core and the first plurality of metal wires; and asecond wire rope and a third wire rope disposed adjacent to andextending longitudinally along the first wire rope.
 13. The cable ofclaim 12, wherein at least one of the second wire rope and third wirerope comprises: a plastic core wire; and a plurality of metal wiresdisposed adjacent to and extending longitudinally along the plastic corewire.
 14. The cable of claim 12, wherein at least one of the second wirerope and third wire rope comprises: a metal core wire; and a pluralityof metal wires disposed adjacent to and extending longitudinally alongthe metal core wire.
 15. A method of making cable for use in a safetybarrier comprising: providing a first plastic core wire; and disposing afirst plurality of metal wires adjacent to and extending longitudinallyalong the first plastic core wire; and prestretching the cable prior toinstallation in the safety barrier.
 16. The method of claim 15, furthercomprising prestretching the cable using a force equal to betweenapproximately 60% to approximately 70% of the force required to breakthe cable.
 17. The method of claim 15, further comprising forming thefirst plastic core wire from a polypropylene thread.
 18. The method ofclaim 15, further comprising wrapping six metal wires adjacent to andextending along the first plastic core wire.
 19. The method of claim 15,further comprising forming a first wire rope with the first plastic coreand the first plurality of metal wires, and disposing a second wire ropeand a third wire rope adjacent to and extending longitudinally relativeto the first wire rope.
 20. The method of claim 19, further comprising:forming at least one of the second wire rope and third wire rope using asecond plastic core wire; and disposing a plurality of metal wiresadjacent to and extending longitudinally relative to the second plasticcore wire.